The poet John Betjeman's "early nip of changeful autumn" is about to arrive with a vengeance in the UK, with ground frost and snow on high ground ending the Indian summer.

Disbelieving chortles over forecasts of an abrupt change will die away as temperatures fall sharply from the pleasantly unseasonal 18.6C (65.4F) reached on Sunday in Southampton and the Royal Horticultural Society's gardens at Wisley, Surrey.

A cold front started pushing towards Scotland, Northern Ireland and northern parts of England and Wales on Monday, making slow but inexorable progress. Icy winds brought rain which turned to sleet and some snow on mountain tops, as forecasters had predicted for the past month.

"Tuesday is when most of us will start to feel a chill in the air," said Andy Ratcliffe of MeteoGroup. "It looks as if there will be strong gusts of wind of up to 70mph along the cold front and also some large rainfalls."

By Wednesday evening, temperatures were expected to fall to 1C (33.8F) across most of the UK, and below freezing in northern areas. The warm weather was fighting a rearguard action, with Monday's highs of 17C (62.6F) falling slowly to a predicted 14C (57.2F) on Tuesday, but all the indicators were pointing steeply down.

"It's going to be pretty cold everywhere across the UK on Wednesday night, with widespread ground frost expected in the whole of the UK and perhaps air frost in places too," said Ratcliffe. On the brighter side, the front is to be followed across the Atlantic by warmer conditions which will bring milder weather at the weekend – but no hope of the record 29C (84.2F) reached at the start of October.

Talk of another cold winter persists but Met Office forecasts stretch only a month ahead, and the weather between now and mid-November is predicted to be "around average for temperatures, rainfall and sunshine". Amateur forecasters continue, however, to point to bumper crops of berries and other signs in the natural world that a big freeze may strike before Christmas.

Record numbers of barnacle geese, known for their yapping cry, arrived with the cold front on Loch Gruinart nature reserve in Islay on Scotland's west coast. The local manager for the RSPB, Jack Fleming, said: "We've got wall-to-wall feathers at the reserve at the moment, it's absolutely incredible. Feeding conditions at the reserve, and probably the weather while the birds were migrating, have brought more of the existing population here at the same time. It's a remarkable spectacle morning and evening."